docs: update CONTEXT.md — control-path wiring, dashboard, decisions 18-21

- §11: dashboard now renders live (SSE/seed/kiosk); GoPro monitoring works;
  flag that camera CONTROL is blocked by the faulty XIAO->ESP command wire
  (status RX works, command TX doesn't). Dedupe the token/default-branch lines.
- §9: add decisions for the MQTT control path, SSE longevity + REST seed,
  nullable status JSON (NaN% fix), and UART being two independent wires.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CONTEXT.md

@@ -193,6 +193,19 @@ reach; the Pi pulls instead.
     Arduino String), recording = byte 29, battery = byte 19; record start/stop =
     `/bacpac/SH?t=<pwd>&p=%01/%00`. ESP-01S flashing needs RST tied HIGH (RST→GND
     holds it in reset) and a known-good UART adapter (verify with a TX↔RX loopback).
+18. **Control path:** `/cameras/{id}/start|stop` publish `{"command":...}` to
+    `remoterig/cameras/<id>/command` via `Subscriber.PublishCommand`; the XIAO forwards
+    it over UART to the ESP-01S. (The handlers used to only write a DB row — no command
+    was ever sent.)
+19. **SSE longevity:** no global `middleware.Timeout` and `WriteTimeout: 0` — a write
+    deadline terminates the long-lived `/events/stream` (it was dying at 10s). The SPA
+    also **seeds** the list via `GET /api/v1/cameras` on mount (SSE only pushes on change).
+20. **Nullable status JSON:** `battery_pct`/`video_remaining_sec` serialized as `null`
+    (not `omitempty`) — omitting them became `undefined` in the SPA → "NaN%".
+21. **UART is two independent wires:** status (ESP `TX/GPIO1` → XIAO `D7`) and commands
+    (XIAO `D6` → ESP `RX/GPIO3`) are separate paths — receiving status does NOT prove
+    the command direction works. Verify the command path with the `set_config`
+    poll-interval test (status rate should change).
 
 ## 10. Conventions
 
@@ -205,17 +218,29 @@ reach; the Pi pulls instead.
 ## 11. Current status & open items (2026-06-05)
 
 **Working / proven on hardware:**
-- Hub up on the Pi (Mosquitto + `remoterig` + SQLite), dashboard on `:8080`.
+- Hub up on the Pi (Mosquitto + `remoterig` + SQLite); **dashboard renders live**
+  (kiosk mode `api_key:""`, SSE kept alive, list seeded via REST on mount).
 - Full CI/CD loop proven: commit → CI build → `dev-latest` → Pi self-update
   (checksum, atomic replace, health-check) → service active.
-- C6 (fw `0.4.0`) joins RemoteRig, connects to the broker, announces as `rig-86d978`,
+- C6 (fw `0.4.0`) self-IDs as `rig-86d978`, registered + listed.
-  and is **registered + listed** in `GET /api/v1/cameras` and the dashboard, with
+- **GoPro monitoring works (Hero 3 Silver):** ESP-01S joins `goprosilver-1`, reads
-  status/heartbeat ingested cleanly. Shows `online:false` / zeros until a GoPro is
+  `/camera/se`, and `online:true` + `battery_raw` + `video_remaining_sec` flow
-  attached (expected on the bench). ESP-01S UART link alive. **End-to-end verified.**
+  GoPro → ESP-01S → XIAO → MQTT → hub → SQLite → API/SSE → dashboard.
+- Hub publishes start/stop commands to `…/<id>/command` (verified on the bus).
 
 **In progress / unresolved:**
-- **GoPro Hero 3 protocol fix** (ESP-01S `fetchStatus` shutter bug) — required before
+- **Camera CONTROL not working — XIAO→ESP command wire is faulty.** Status (ESP→XIAO,
-  real battery/recording data; needs a real Hero 3.
+  `GPIO1→D7`) works, but the command direction (XIAO `D6` → ESP `RX/GPIO3`) does not,
+  so `start_recording`/`set_config` never reach the ESP. Confirmed via the `set_config`
+  poll-interval test (status rate didn't change). Fix/re-seat that one jumper; then
+  Record + live config will work. (See decision #21.)
+- **Battery calibration:** `battery_raw` (~56–59) flows; set `set_battery_cal`
+  (`raw_min/raw_max`, provisionally 0/100) for `battery_pct` — but this is a *command*,
+  so it's blocked by the same XIAO→ESP wire above. `video_remaining` offset (25-26)
+  provisional. SPA now shows "N/A" (not "NaN%") when `battery_pct` is null.
+- **Pi SD-card health:** a transient `Input/output error` on core binaries cleared on
+  reboot — watch for recurrence (failing card); re-image via `setup-pi.sh` if it
+  returns (everything is reproducible from git).
 - **Rotate the Gitea runner registration token** (was exposed in a setup paste).
 - Gitea repo **default-branch HEAD** points at a nonexistent ref — set default branch.
 - Optional: clear the stale **retained** MQTT message at